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United States Patent |
5,509,355
|
Stewart
,   et al.
|
April 23, 1996
|
Low energy fuse and method of manufacture
Abstract
A low energy fuse is extruded as a single ply primary tube 1 from a plastic
resin blend with particulate energetic material 2 being internally
distributed in a manner known per se, said resin blend comprising a major
amount of an orientable polymer, for example, linear low density
polyethylene to provide structural integrity and a minor amount of a
modifier to impart enhanced particle retentive properties to the tube and
preferably also containing a polymer or copolymer to impart melt strength
and aid in tube extrusion.
Inventors:
|
Stewart; Ronald F. (Ayr, GB6);
Welburn; David J. (Brownsburg, CA);
Welsh; David M. (Brownsburg, CA);
Greenhorn; Robert C. (L'Original, CA)
|
Assignee:
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Imperial Chemical Industries PLC (London, GB)
|
Appl. No.:
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932089 |
Filed:
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August 19, 1992 |
Foreign Application Priority Data
Current U.S. Class: |
102/275.8; 102/275.1; 102/275.11 |
Intern'l Class: |
C06C 005/04 |
Field of Search: |
102/275.1,275.3,275.5,275.8,275.9,275.11,275.12
|
References Cited
U.S. Patent Documents
2891475 | Jan., 1957 | Blair et al. | 102/215.
|
2993236 | Jul., 1961 | Brimley et al. | 86/1.
|
3311056 | Mar., 1967 | Noddin | 102/275.
|
3590739 | Jul., 1971 | Persson | 102/275.
|
3698280 | Oct., 1972 | Welsh | 102/275.
|
3867884 | Feb., 1975 | Langrish et al. | 102/275.
|
4290366 | Sep., 1981 | Janoski | 102/202.
|
4328753 | May., 1982 | Kristensen et al. | 102/275.
|
4369688 | Jan., 1983 | Yunan | 102/275.
|
4493261 | Jan., 1985 | Simon et al. | 102/331.
|
4607573 | Aug., 1986 | Thureson et al. | 102/275.
|
4660474 | Apr., 1987 | Dias dos Santos | 102/275.
|
4699059 | Oct., 1987 | Kelly et al. | 102/215.
|
4756250 | Jul., 1988 | Dias dos Santos | 102/275.
|
4757764 | Jul., 1988 | Thureson et al. | 102/275.
|
4817673 | Apr., 1989 | Zoghby et al. | 102/275.
|
5010821 | Apr., 1991 | Blain | 102/275.
|
Foreign Patent Documents |
1378669 | Dec., 1974 | GB.
| |
2027176 | Feb., 1980 | GB | 102/275.
|
1566107 | Apr., 1980 | GB.
| |
WO8703954 | Jul., 1987 | WO.
| |
Primary Examiner: Johnson; Stephen M.
Attorney, Agent or Firm: Cushman Darby & Cushman
Parent Case Text
This is a division of application No. 07/581,411, filed Sep. 12, 1990 now
abandoned which is a continuation of application Ser. No. 07/306,013,
filed Feb. 3, 1989 now abandoned.
Claims
We claim:
1. A cold drawn low energy shock wave conductor comprising an extruded
single-wall, dimensionally stable plastic tube having an inner surface
coated with a particulate reactive energetic material, the plastic of the
tube comprising a homogeneous extrudable blend of a major amount of a draw
orientable polymer resin lacking adequate reactive material-retaining
properties, and a minor amount of a modifier which is a miscible or
compatible material which imparts an enhanced reactive material-retaining
capability to the inner surface of said extruded plastic tube.
2. A shock wave conductor according to claim 1 wherein said polymer resin
is in the form of a continuous matrix and the modifier is distributed in
the matrix polymer such that it has a greater concentration at said inner
surface of the tube than in the body of the matrix.
3. A shock wave conductor according to claim 2 wherein said modifier is
present as non-contiguous particles or fibrils within the matrix.
4. A shock wave conductor according to claim 3 wherein said particles are
about 0.5.mu. in size.
5. A shock wave conductor according to claim 2 wherein said modifier is
concentrated in segregated zones in the matrix.
6. A shock wave conductor according to claim 1 wherein the polymer resin is
a fibre forming a polymer.
7. A shock wave conductor according to claim 1 wherein the polymer resin is
selected from the group consisting of (1) addition polymers and
condensation polymers having a substantially linear hydrocarbon backbone
structure; (2) such polymers wherein the backbone structure is interrupted
by hetero atoms; (3) such polymers wherein the backbone structure is
substituted by polar functional groups and such polymers wherein the
backbone structure is interrupted by hetero atoms and substituted polar
functional groups.
8. A shock wave conductor according to claim 7 wherein the addition polymer
is selected from the group consisting of a polyolefin homopolymer and
polyolefin copolymer.
9. A shock wave conductor according to claim 7 or 8 wherein the addition
polymer is selected from the group consisting of a copolymer of ethylene
and a copolymer of an alpha-olefin with a substituted olefin monomer.
10. A shock wave conductor according to claim 7 wherein the condensation
polymer is selected from the group consisting of a polyester and a
polyamide.
11. A shock wave conductor according to claim 1 wherein said modifier is
selected from the group consisting of a homo-polymer, a copolymer resin,
and a material of lower molecular weight than the homopolymer and
copolymer resin but of like properties.
12. A shock wave conductor according to claim 11 wherein the modifier is
selected form the group consisting of ionomers, ethylene/acrylic acid
(EAA) copolymers, ethylene/methacrylic acid (EMA) copolymers,
polyisobutylenes (PIB), polybutadienes (PBD), polyethylene waxes (PE Wax),
polyethylene glycols (PEG), poly-propylene glycols (PPG), ethylene vinyl
alcohol resins (EVAL), butyl rubber, Rosin, maleinised polypropylene,
polyacrylamide or poly-acrylamide oxime resins, polyethylene imine,
sulphone and phosphonate resins.
13. A shock wave conductor according to claim 11 wherein the modifier is
selected from the group consisting of ethylene/acrylic acid (EAA)
copolymers, ethylene/methacrylic acid (EMA) copolymers and neutralised
ionomers thereof.
14. A shock wave conductor according to claim 11 wherein the modifier is
selected from the group consisting of polyisobutylenes (PIB),
polybutadienes (PBD), polyethylene waxes (PE Wax), polyethylene glycols
(PEG), poly-propylene glycols (PPG), ethylene vinyl alcohol resins (EVAL),
butyl rubber, Rosin, maleinised polypropylene, polyacrylamide,
poly-acrylamide oxime resins, polyethylene imine, sulphone and phosphonate
resins.
15. A shock wave conductor according to claim 11 wherein the modifier is
selected from the group consisting of ethylene/acrylic acid (EAA)
copolymers, ethylene/methacrylic acids (EMA) copolymers and partially and
wholly neutralized monomers thereof.
16. A shock wave conductor according to claim 1 comprising a minor amount
of a homopolymer or copolymer resin or cross-linking agent which is
miscible in or compatible with said orientable polymer resin and which
imparts melt strength and aids in tube extrusion.
17. A shock wave conductor according to claim 16 wherein the melt
strength/extrusion improving resin is selected from the group consisting
of ethylene/vinyl acetate copolymers and copolymers of ethylene with lower
alkyl esters of acrylic or methacrylic acid.
18. A shock wave tube according to claim 1 having a tensile strength of up
to 170 newtons per square millimeter.
19. A shock wave conductor according to claim 1 wherein the coreload is
from about 15 to 60 mg.m.sup.-1.
20. A shock wave conductor according to claim 1 wherein the coreload is up
to about 20 mg.m.sup.-1.
21. A shock wave conductor according to claim 1 wherein the tube has
dimensions of from 2.5 to 3.3 mm O.D. and about 1.3 mm I.D.
22. A shock wave conductor according to claim 1 wherein the tube is treated
externally with agents to improve resistance to water or oil or to water
and oil.
23. A shock wave conductor according to claim 1 wherein the polymer resin
is a condensation polymer having a substantially linear hydrocarbon
backbone structure interrupted by hetero atoms.
24. A shock wave conductor according to claim 9 or claim 23 wherein the
polymer resin has a substantially linear hydrocarbon backbone structure
substituted by polar functional groups.
25. A low energy shock wave conductor in the form of a cold drawn extruded
single wall, dimensionally stable plastic tube having an inner surface
coated with particulate reactive energetic material formed according to
the method which comprises
(a) extruding a polymeric melt through a wide annular die in the form of a
thick walled tube while distributing particulate reactive energetic
material in a core load per unit of length on the inner surface of the
thick walled tube, the polymeric melt comprising a substantially
homogenous blend of a major amount of a draw orientable melt-extrudable
polymer resin and a minor amount of a miscible or compatible material as
an adhesion promoting agent which is distributed in the extruded melt such
that it has a greater concentration at the inner surface of the tube than
in the body of the extruded melt and imparts an enhanced reactive
energetic material-retaining capability to the inner surface of the
extruded tube, and
(b) cold drawing the thick walled tube to elongate and form a localized
drawing point to increase tube tensile strength, reduce wall thickness,
and to reduce core load per unit length of the reactive energetic
material.
26. A low energy shock wave conductor according to claim 25 in the form of
a cold drawn extruded single wall, dimensionally stable plastic tube
having an inner surface coated with a particulate reactive energetic
material wherein the polymer melt further comprises a minor amount of a
homopolymer or copolymer resin which is miscible in the polymer melt and
which imparts melt strength and aids in tube extrusion.
27. A low energy shock wave conductor comprising a cold drawn,
dimensionally stable tube made of extrudable plastics material, and
containing a core loading of a particulate reactive energetic material,
wherein the said tube has an extruded single-wall, and throughout its
length an inner surface circumscribing a void through which a shock wave
may be transmitted, the said surface retaining said particulate reactive
energetic material as a layer thereon, and the said plastics material
comprises a substantially homogeneous blend of a major amount of a draw
orientable polymer resin lacking adequate reactive material-retaining
properties, and a minor amount of a modifier which is a miscible or
compatible material which imparts an enhanced reactive material-retaining
capability to said polymer resin.
28. A low energy shock wave conductor comprising an extruded single-wall,
dimensionally stable plastic tube having an inner surface coated with a
particulate reactive energetic material, the plastic of the tube
comprising a homogeneous extrudable blend of a major amount of a draw
orientable polymer resin lacking adequate reactive material-retaining
properties, and a minor amount of a modifier which is a miscible or
compatible material which imparts an enhanced reactive material-retaining
capability to the inner surface of said extruded plastic tube wherein the
polymer resin is a continuous matrix and the modifier is present as
fibrils a few microns in length with aspect ratios of from about 6 to
about 10 aligned with the tube axis and distributed in the matrix polymer
such that it has a greater concentration at the inner surface of the tube
than in the body of the matrix.
29. A cold drawn shock wave conductor according to claim 28.
Description
The present invention relates to an improved, low energy fuse for use in
commercial blasting, improved materials useful in its manufacture and to a
method for producing such a fuse.
The use of non-electric explosives initiation systems is now well known in
the blasting art. Generally, these systems comprise the use of one or more
lengths of detonating fuse cord each having attached at one end thereof an
instantaneous or delay blasting cap. When the opposite end of the cord is
initiated by means of an explosive initiator, such as a cap or priming
trunk line fuse cord, the detonating fuse is detonated and an explosive
wave is transmitted along its length at high velocity to set off the
attached blasting cap. The use of such a system is generally chosen where
there may be hazards involved in using an electric initiation system and
electric blasting caps.
In the past, many improvements have been made in the quality and
reliability of non-electric initiation systems and in detonating fuse
cord. An early but significant development was disclosed in our British
patent No 808 087 (equals U.S. Pat. No. 2,993,236). This provided a
solution to the problem of how to safely incorporate an explosive core in
a thermoplastic tubular sheath during extrusion. The technique disclosed
therein can be widely applied to production of tubular products for use in
initiation systems. One such product is shown in British Patent No. 1 238
503 (equals U.S. Pat. No. 3,590,739; CA 878 056) which discloses a
detonating fuse which comprises a tube having only a thin layer of a
reactive substance coated on the inner area thereof rather than a core.
Such a fuse is marketed under the registered trade mark "NONEL". Commonly,
this type of fuse has come to be known as a shock wave conductor and will
be referred to as such hereinafter.
The production of shock wave conductors of small diameter has been
restricted to use of a limited number of polymers due to the principal
properties sought for the product. The product development trend in the
art to meet such problems has been to provide laminated plastics tubes
comprising an inner and outer layer of differing plastics to satisfy
requirements of reactive substance adhesion and mechanical strength
respectively. A shock wave conductor in the form of a two-ply laminated
tube, the outer ply of which provides reinforcement and resists mechanical
damage, is disclosed in GB 2 027 176 (U.S. Pat. No. 4,328,753; CA 1 149
229). Likewise in U.S. Pat. No. 4,607,573, a method is described for the
manufacture of a two-ply or multiply shock tube wherein the outer covering
is applied only after the inner tube has been stretched to provide the
desired core load per unit length. Further examples of such over coated
tubes are disclosed in U.S. Pat. No. 4,757,764 which proposes use of the
tubes of the type disclosed in the above-mentioned U.S. Pat. No. 4,607,573
with non-self-explosive reactive material within the tube. Other
disclosures of the use of non-self-explosive reactive material are to be
found in Brazilian Patent No. PI 8104552, CA 878 056, GB 2 152 643 and
U.S. Pat. Nos. 4,660,474 and 4,756,250.
While the invention of the shock wave conductor has been an important
contribution to the art of blasting, the known shock wave conductors are
not without disadvantages. Since the reactive substance within the tube
only comprises a thin surface coating which adheres to, but is not bound
to the tube, then only certain special plastics have in practice been
found suitable to provide the necessary adhesion. Such special plastics
tend to be both expensive and to lack mechanical strength. When protected
by an outer layer of material, as disclosed in U.S. Pat. Nos. 4,328,753
and 4,607,573, the mechanical properties are improved.
SUMMARY OF THE INVENTION
A need has arisen, therefore, for a shock wave conductor which retains all
the explosive properties of the tubes currently in use and which is also
possessed of great mechanical and tensile strength but at low production
cost.
According to the present invention, a low energy shock wave conductor is
provided which comprises an extruded single-wall, dimensionally stable
plastic tube having an inner surface coated with a particulate reactive
energetic material, the plastic of the said tube comprising a
substantially homogeneous blend of a major amount of a draw orientable
polymer resin lacking adequate reactive material-retaining properties, and
a minor amount of a modifier which is a miscible or compatible material
which imparts an enhanced reactive material-retaining capability to the
said extruded plastic tube.
Most favourable results are achieved in most instances when the polymer is
substantially orientated linearly and this is best achieved by cold
drawing the tube after melt consolidation. As used herein the term "cold
drawing" means irreversible extension with a localised draw point of the
extruded tube at any stage after the polymer has left the extruder and
cooled sufficiently to consolidate a permanent tubular structure but
remains plastic or sufficiently so to permit stretching under applied
stress to thereby orientate the crystallites in the direction of tube
length. Thus cold drawing may be carried out at any stage after the tube
has taken shape after extrusion and has begun to cool from its extrusion
temperature. Therefore it should be noted that the temperature of "cold
drawing" lies suitably in the range of from about ambient room temperature
to about 180.degree. C. or higher depending on the polymer(s) chosen and
it will be recognised that the temperature profile of the cold drawing
stage(s) need not be uniform so that the post-extrusion temperature
treatment of the tube may be variable. Additionally, intermediate or
terminal relaxation stages may be employed, as are well known in the
synthetic fibre art, to "stress relieve" the cold drawn tube and thereby
impart improved dimensional stability to the tube. It is envisaged that
normally artificial cooling of the extruded tube will be applied such as
forced air and/or water cooling to control the temperature during post
extrusion treatment. The resulting tube is safe to handle and is easily
reeled for storage or transport. Of course the finished tube may be
treated externally with agents to improve resistance to water and oil,
especially diesel, permeability. Ordinarily a thin film or coating will
suffice. Alternatively, the polymer blend may include a further resin to
improve oil resistance. The tube can be overcoated with another layer of
polymer as in the prior art tubes but there is no perceived advantage in
doing so.
Tests, including microscopic examination, carried out on the improved tubes
made so far in accordance with the invention indicate that the
draw-orientable polymer resin is in the form of a continous matrix whilst
said compatible material is mostly present within the matrix as discrete
noncontiguous particles, sized about 0.5 .mu., or fibrils a few microns in
length, with aspect ratios typically of from about 6 up to about 10
oriented along the tube axis. The structural state of said miscible
material is less certain because inherently there are no clear phase
boundaries to be highlighted by electron microscopy. However we have noted
that those miscible polymeric materials that impart good particle adhesion
properties at the inner tube surface appear to be present to a substantial
extent as indistinctly segregated zones of more concentrated material.
Thus electron microscopy (viewing regions up to 20 .mu. across) reveals
arbitrary random microstructure in the plastic matrix consistent with such
zoning. It has further been observed that in many instances the miscible
or compatible material is, following melt extrusion, distributed such that
it has a greater concentration at the inner surface of the tube than in
the body of the matrix which provides optimum exposure to interaction with
the reactive material and favorable performance in the resulting shock
wave conductor. The distribution of the miscible or compatible material
will vary depending on the physical and chemical properties of the
selected material.
The polymer tube components may be pro-blended in a suitable mixer prior to
supply to the melt extrusion equipment to ensure proper mixing of material
with the matrix polymer. The observed surface enrichment upon melt
extrusion is a surprising effect and provides a surface presence of the
desired powder adherent material substantially larger than the population
of components in the tube material would imply. This phenomenon is
believed to be achievable by a number of mechanisms, or a helpful
combination of such mechanisms, depending on the particular polymer matrix
and powder adherent materials present. Presently favoured explanations are
first preferential wetting or coating of the extrusion die surfaces by the
dispersed material in the molten polymer matrix, and second migration of
material under shear gradients in the extrusion head to the die head
surface, i.e. rheological causes. The evidence of inner surface enrichment
both in the as-extruded tube and that following cold drawing is
scientifically demonstrable by use of well known physical techniques such
as ESCA.
DETAILED DESCRIPTION OF INVENTION
The miscible or compatible material is preferably a miscible or compatible
polymer or copolymer resin or a lower molecular weight material of like
properties capable of improving reactive material-retaining properties of
the matrix polymer by one or more of the following mechanisms; (i)
chemical interaction such as ionic or hydrogen bonding; (ii) physical
interaction such as polar attraction, tack or surface-wetting and (iii)
electrostatic interaction with the selected reactive material. In fact
virtually any material which can be successfully introduced to the bulk
matrix-forming polymer and survive the extrusion process without
degenerating or disrupting the formation of the tube can be used provided
it has the capability to impart the desired improvement in reactive
material-retaining property to the matrix polymer. Suitable materials can
be recognised by their compatibility with the selected bulk resin and by
having pendant or free functional groups which will interact with the
chosen reactive material by e.g. polar attraction, hydrogen bonding, ionic
attraction without necessarily forming an ionic bond. Alternatively the
molecular structure is such that interaction is by physical attributes
such as tack, high surface energy or surface conditions e.g. roughness
which could be modified by inclusion of ultrafine fillers such as silica
at levels of perhaps 0.5-1.0%.
The bulk polymer matrix of which the tube is mainly composed broadly
comprises olefinic polymers, including ethylene/alpha-olefin copolymers
where the olefin monomer may have from 4 to 16 carbon atoms such as
1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene etc. These typically have
a melt flow index of from 0.1 to 2 and a density of from 900 to 950
kg.m.sup.-3. In general suitable matrix polymers will be fibre forming
polymers. Advantages of these polymers are their ease of processing in
extrusion equipment, structural strength and generally lower cost than
current shock tube components.
The plastic preferably also comprises a minor amount of a polymer or
copolymer resin or cross-linking agent which is miscibie in the said
matrix polymer resin and which imparts melt strength and aids in tube
extrusion. Such a material may be an ethylene/acrylic acid ester copolymer
or a copolymer of ethylene and vinyl acetate. The acrylic esters are
preferably lower alkyl esters such as methyl or butyl acrylates.
Thus a suitable tube comprises a blend of 60 to 97% by weight of a
polyolefin resin, e.g. linear low density polyethylene, (optionally
including from 5 to 45% weight of a second resin which is a
polyolefin-miscible or compatible polymer, copolymer or cross-linking
agent which imparts melt strength to the blend and aids in tube extrusion)
and from 2 to 25%, preferably up to 10%, by weight of a third
polyolefin-miscible or compatible resin which is a surface property
modifying polymer or copolymer such as an ethylene/acrylic acid or
methacrylic acid copolymer which may be wholly or partially neutralized
e.g. an ionomer such as Surlyn 1855 (Trade Mark for a Du Pont product).
A linear low density polyethylene which may constitute up to about 97% of
the polymer blend and which is used in a preferred embodiment of the tube
of the invention desirably has a melt flow index (MFI) of around 1.0. The
polyethylene-miscible or compatible resin which imparts melt strength to
the polymer blend can advantageously be, for example, ethylene/vinyl
acetate copolymer or a low density polyethylene having a melt index of 3
or less. The polyethylene-miscible or compatible powder-retention
enhancing resin may be any acidic or ionomeric-based co-polymer such as,
for example, PRIMACOR, an ethylene-acrylic acid copolymer, sold by Dow
Chemical Company.
The method of the invention comprises the steps of extruding a melt of the
blended constituents of the plastic tube through a wide annular die in the
form of a thick walled tube while distributing particulate reactive
energetic material in a core load per unit length on the inner wall of
said thick walled tube and elongating the said thick walled tube to form a
localized drawing point by cold drawing, to increase the tube tensile
strength, to reduce the said wall thickness and to reduce the core load
per unit length of the said reactive material. The manner of extruding the
thick walled tube whilst introducing the core load of reactive material is
similar to that disclosed in GB 808 087 (U.S. Pat. No. 2,993,236) and is
widely understood by those in this art. The sizes for shock tube are
virtually standardized throughout the art at approximately 3 mm O.D. and 1
mm I.D. by the need for compatibility with existing detonators etc. Thus
it will be apparent to those skilled in the art that sizing dies, where
required, amount of melt drawing and cold drawing will be selected to
provide an equivalent or different sized product. It may be suitable to
start from extrusion of a primary tube of about 6 to 10 mm O.D. and about
3 mm I.D. Significant drawing below tube consolidation temperatures may be
most appropriate. However in view of the diversity of compositions now
discovered to be useful for producing such tubes it is not considered that
definite ranges can be specified for drawing. However a natural draw ratio
of at least 4:1, weight for weight of equal lengths of undrawn against
drawn tube, may be most favorable which is perhaps equivalent to a
mechanical draw ratio of about 5 to 8:1 Therefore, due consideration must
be had to the type of matrix polymer chosen and any necessary minor
operating adjustments ascertained by brief preliminary trial or
experimentation. Guidelines for same may be determined from the
non-limitative Examples hereinafter given.
The plastic tube shock wave conductor is preferably manufactured in such a
manner as to provide a tensile strength of up to 170 newtons per square
millimetre. An effective minimum coreload for high velocity shock tubes
would be about 15 mg.m.sup.-1 but loadings of reactive material of up to
20 mg.m.sup.-1 are possible, or even higher as indicated in the
above-mentioned specifications e.g. 25 to 60 mg per linear meter as
indicated in U.S. Pat. No. 4,757,764. Tube dimensions are a matter of
choice and would be affected by the required internal diameter and the
need to obtain a self-supporting tube but normally these would be from 2.5
to 3.3 mm O.D. and about 1.3 mm I.D.
Suitable materials for use as the draw orientable matrix polymer include
linear polyethylenes such as those currently commercially available under
the Trade Marks "Aecithene", particularly LF 3020, LF 3081 and LF 3100;
"Dowellex", especially 2045-A, 2049 and 2075; Du Pont 12J1; Esso 3121.73;
Idemitsu polyethylene-L 0134H; Mitsubishi polyethylene-LL H20E, F30F and
F30H; Mitsui "Ultzex" 2020L, 3010F and 3021F; Nippon NUCG-5651 and Union
Carbide DFDA-7540, which are all believed to be essentially LLDPE's, but
equally MDPE, HDPE, ULDPE and LDPE can also be used to form plastic tubes
in a satisfactory manner. Blends of these polyolefins are also considered
useful, especially LLDPE with HDPE due to their close compatibility which
is believed to arise from cocrystallisation. Ethylene/propylene copolymers
such as EXXELOR.TM. PE 808 (Exxon Chemicals Ltd.) and polypropylenes such
as PROPATHENE.TM. (ICI) are also useful for the present purpose. Likewise,
copolymers of these polyolefins with substituted olefins is possible.
Due to variations in commercially available bulk polymers some initial
experimentation and minor variation of the extrusion process may be
required but such is believed to be within the ordinary skill of those in
the art. Apart from the above olefinic polymers which are favored in terms
of availability, cost, processability and physical properties, when
extruded to form a shock tube, other draw-orientable melt-extrudable
polymers of sufficient toughness and possessing adequate water and oil
resistance may be used e.g. polyesters such as
polyethylene/butyleneterephthalate (PBT) or nylons may also be used as a
basis for the structural polymer matrix of the tube with similar results.
Kodar.TM. is a suitable polyester obtainable from Eastman Chemicals. The
diversity of polymers available in the plastics extrusion-moulding field
and synthetic fibre field is now so vast that it is impossible to test
them all but the expertise available in those fields will permit an
informed exploration of other polymers should that be desired.
The polymer that provides the bulk matrix of the tube is simply required to
provide a tough tube of the desired dimensions and physical properties and
to be an adequate carrier for the incorporated material that serves to
impart powder adherent/retentive properties to the inner tube surface. It
needs, of course, to be melt extrudable in a manner allowing effective
powder introduction and therefore to possess, or be given, adequate melt
strength. Many of the preferred bulk polymers, e.g. LLDPEs, are
melt-thinning under shear and therefore require either highly skilled
extrusion expertise or, if a more forgiving polymer melt is desired, a
sufficient but small proportion of melt blended miscible melt strength
additive as described further below.
The basic and surprising discovery from which the present invention is
derived is that for a practical shock wave conductor tube a bulk powder
adherent homopolymer is not needed contrary to the long standing belief
and practice of the art. A blend in which there is separation of function
can work as well or better and be economically advantageous.
The particulate reactive material required for sustaining a shock wave
within the tube requires the surface presence of an additive which
according to the present invention may be in the form of another polymer,
or a lower molecular weight material, which is sufficiently miscible or
compatible as to be incorporated in the bulk polymer matrix to provide an
extruded tube exhibiting the desired retentive properties. The additive
must not be excessively binding nor exhibit aggressive tack or rely solely
on transient electrostatic properties since the reactive material would
then be incapable of propagating the shock wave either by being
permanently attached to the tube surface or through migration from the
surface over a period of storage. Thus we have found that selected
materials should be added to the matrix polymer prior to extrusion to
provide an extrudable blend capable of being drawn to form a satisfactory
tube for use as a shock wave conductor. These are characterized by having
pendant or free functional or polar groups e.g. carboxyl, anhydride,
hydroxyl, halogen, cyano, amido, sulphonate etc., by having an inherent
adherent property or by being of relatively small molecular size. Such
materials can be selected from ethylene/acrylic acid (EAA) copolymers,
ethylene/methacrylic acid (EMA) copolymers, polyisobutylenes (PIB),
polybutadienes (PBD), polyethylene waxes (PE Wax), ionomers, polyethylene
glycols (PEG), poly-propylene glycols (PPG), ethylene vinyl alcohol resins
(EVAL), buryl rubber, Rosin, maleinised polypropylene, polyacrylamide or
polyacryl-amide oxime resins, polyethylene imine, sulphone or phosphonate
resins. Preferably the additive is an ethylene acrylic acid copolymer
(EAA) or methacrylic acid copolymer (EMA), or an ionomer. Polymers
suitable for this purpose include those commercially available under the
Trade Marks "Primacor" (EAA), e.g. 1430, "Surlyn" 1855 (believed to be
wholly or partially neutralized polymers of methyl acrylic acid and
ethylene monomer) or 8940 (Na ionomer), "Nucrel" (EMA) 403 or 410, Hyvis
30 (PIB, BP Chemicals), Lithene N4 6000 (PBD, Doverstrand Ltd), Soarnol D
(EVAL resin, British Trades & Shippers), Portugese WW Gum Rosin from Mead
King Robinson Co Ltd, PEG 4000 (Lanster Chemicals) and lower molecular
weight materials such as PE wax (AC 617A NE 3569, Allied Chemicals) are
also effective.
The terms "miscible" and more especially "compatible" should not be
understood in any narrow sense of being free of all tendency (in The
absence of other forces) to separate or segregate. Thus ionomers such as
those sold under the Trade Mark "Surlyn" are not considered miscible with
LLDPEs, nor are they promoted as being compatible with LLDPEs. However we
have shown that under the high stress mixing and shearing forces
experienced in a screw extruder they can be finely and homogeneously
dispersed to levels of say 10% w/w and any inherent tendency to segregate
or for droplets to coalesce into large globules does not adversely
manifest itself in the short duration of extrusion prior to consolidation
of the tube.
The polyethylene-miscible or compatible resin which imparts melt strength
to the polymer blend can be, for example, ethylene/vinyl acetate copolymer
such as CIL 605-V or ethylene/methyl acrylate or ethylene/butyl acrylate
(EMA or EBA esters) or a low density polyethylene having a melt index of 3
or less. Lupolen 2910 M is a suitable EBA ester obtainable from BASF (UK)
Ltd.
Of course these polymers may include typical additives such as flame
retardants antioxidants fillers, slip and anti-blocking agents, coupling
agents, U.V. stabilizers, thickeners and pigments as required.
BRIEF DESCRIPTION OF DRAWINGS
A better understanding of the details of the invention will be obtained
from the following description and the accompanying drawings in which:
FIG. 1 is a transverse cross-section, not to scale, of the shock wave
conductor of the invention; and
FIG. 2 is a flow diagram illustrating the manufacturing steps employed in
the method of the invention.
Referring to FIG. 1, a cross-section of the shock wave conductor of the
invention is shown wherein 1 is the tubing wall which comprises one of the
heretofore described plastic blends and 2 is a thinly distributed deposit
of reactive or energetic material.
Referring to FIG. 2, the steps involved in the method of manufacture of The
shock wave conductor of FIG. 1 are illustrated. Plastic resin storage
hoppers P1, P2 and P3 contain, respectively, particulate polyolefin resin,
optional particulate resin which imparts melt strength and particulate
resin which enhances powder retention. The resins from P1, P2 and P3 are
proportioned into resin blender 10 and the blended resin is transferred to
extrusion apparatus 11. Extrusion apparatus 11 produces a continuous,
thick-walled primary tube having an initial inner and outer diameter
greater than that desired in the final tube product. As the thick-walled
tube is produced, an energetic reactive material, for example, a powdered
mixture of HMX and aluminium from reservoir 12, is distributed by known
means on the inner surface of the tube at a core load of about 2-3 times
that of the desired final tube product. The extruded thick-walled,
energetic material-containing tube is then directed, as melt drawdown
takes place, to a cooled, size-determining die 13 from which it emerges as
a reduced diameter tube. After The drawdown size reduction, the tube is
passed through a spray cooler 15 and, then, to an elongation/stretching
station 16. Stretching station 16 preferably comprises a pair of capstans,
the downstream, fast-moving capstan rotating 5 to 6 times more rapidly
than the upstream slow-moving capstan in order to provide a corresponding
elongation of the tube, and to eliminate bumpy areas and increase tensile
strength. Heat from heating unit 14 may optionally be required. After
stretching at station 16, optional cooling is provided at cooling unit 17
and, if desired, optional stress relief (not shown) may be given and the
final product is collected at station 18.
The position and functioning of sizing die or plate 13 is in many instances
critical to the geometry and, hence, to the performance of the final
finished product. The final tubing dimensions may be from 2.5 mm to 3.3 mm
outside diameter and about 1.3 mm inside diameter. Plate or die 13 governs
the size and shape of the product subsequently produced at stretching
station 16. Any fluctuations in the tubing leaving die plate 13 tend to be
preserved through the subsequent stretch operation. Die plate 13 may
comprise, for example, a metal split ring equipped for water cooling and
lubrication, a series of such rings or a vacuum sizing device. The large
slow moving primary capstan at station 16 is important both to provide
control of the drawdown ratio of the primary tube and to provide
sufficient surface area and drag to prevent slippage and/or
"free-wheeling" during the stretching operation. The stretch ratio is
critical to the achievement of the ultimate tensile strength of the
product while maintaining adequate size control and eliminating excessive
stretch in the final product. The addition of reactive material to the
large tube at station 12 is controlled so that the final tubing core load
is in the order of 10-30 mg/m. However circumstances could call for higher
loadings as is known in the art in which case appropriate adjustments
would be made.
The plastic blend, e.g. 80/10/10, preferably comprises linear low density
polyethylene (LLDPE) as the major component and, for example, ethylene
vinyl/acetate copolymer (EVA) and ethylene/acrylic acid copolymer as minor
components. The LLDPE gives tensile strength to the final product, the EVA
provides melt-strength in order to extrude more easily a uniform product
and the ethylene acrylic acid copolymer imparts enhanced powder adhesion.
It will be recognized by those skilled in the art that a reduced melt
drawdown ratio may obviate the need for a melt strength enhancer or may
require less of it. Further, the melt-strength requirement and the powder
adhesion capability, may, in some instances, be provided by a single resin
suitably possessing both attributes e.g. selected EVAs. The addition of
the ethylene/acrylic acid copolymer at 10% w/w to the blend gives
excellent powder adhesion to the tubing, and levels well in excess of 4.3
g of powder per square meter of inner tube area are readily achievable.
The tensile strength of the shock tube of the invention is high compared
with any known prior art shock tube. Tubing of 3.0 mm O.D. and 1.3 mm I.D.
requires a load of between 90 kg and 100 kg to break it at about 100%
elongation. This translates to a tensile strength of 150 to 170 N/mm.sup.2
(20,000 to 25,000 psi). Stress-relieving will reduce tensile strength and
increase elongation to break.
It will be understood that, during the manufacturing process, various
quality control testing and inspections are performed to ensure that the
core load of reactive material is within the specified range and that the
dimensions of the tube are uniform and within narrow limits.
The invention will now be further described by way of the following
non-limitative Examples. Example 1 is a comparative Example not in
accordance with the invention.
EXAMPLE I
A blend of LLDPE (85%) and low functionality (2%) EVA (15%) was extruded by
a Battenfelder extruder (5.0 cm diameter, 24:1 1/d metering screw),
through a 3.0 cm outer die and a 1.4 cm inner mandrel. The melt was
subjected to a 15:1 drawdown over 25 cm through a 7.6 mm diameter sizing
die and processed as shown in FIG. 2. The optional heating and cooling
were not used. The large tube dimensions were about 7.6 mm O.D. extruded
at a rate of about 5 m per minute.
After stretching, the tube size was about 3 mm O.D. and produced at a rate
of 45 m per minute. Explosive powder (HMX/A1) was added to the large tube
at a rate sufficient to give a final core load of about 20 mg/m (4.4
g/m.sup.2 of internal area). The tensile strength of this tube was about
140 N/m.sup.2. A break load of 80 kg was required at an extension of 160%.
Oil resistance was somewhat better than that of regularly produced
mono-plastic shock tubing. Powder adhesion was, however, very poor after
vibration and handling of the tubing
EXAMPLE II
A blend of LLDPE (80%), EVA (10%) and EAA (10%) was extruded, cooled and
stretched as described in Example 1. The tensile strength of this tube was
170 N/m.sup.2. A break load of 100 kg was required over an extension of
130%. Oil resistance was unchanged from Example 1. Powder adhesion was
over 4.4 g/m.sup.2 and approached 7 g/m.sup.2.
EXAMPLE III
A portion of the tubing of Example II was stretched by applying the
optional heating and cooling stages. No essential differences in tubing
properties were observed.
EXAMPLE IV
A blend of LLDPE (67%), EVA (16.5%) and EAA (16.5%) was extruded under the
same conditions as Example I. All physical properties were maintained
except elongation which was about 100%.
EXAMPLE V
A blend of 80% Dowellex 2045-A, MFI 1.0, density 0.920 g/cc, (an
octene-based LLDPE); 10% CIL-605-V, MFI 0.15, density 0.923 g/cc (an EVA
copolymer containing 2% VA); and 10% Dow Primacor 1430, MFI 5.0, density
0.938 g/co, (EAA copolymer containing 9% acrylic acid), i.e. an 80/10/10
blend of LLPDE/EVA/EAA, produced a very useful plastics composition which
was extruded into tubing. Likewise 90/8/2, 90/10/0, 90/0/10 (no sizing
dies), 66/17/17 and 85/15/0 compositions were produced and formed into
tubes. The extrusion temperature profile ranged from about 150.degree. C.
to 190.degree.. Melt draw down ratios were 14:1 or less. An extrusion die
of approximately 30 mm with a mandrel die of about 14 mm was used.
Appropriate sizing dies improved uniformity of tube size. The average
coreload of reactive material was about 22 mg.m.sup.-1. The extruded tube
was cold-drawn using a second capstan rotating at around 5-6 times the
surface speed of the feed capstan such that the localised draw point or
neck was at the point of departure from the feed capstan. Terminal line
speed was 40-45 m/min. The true cold draw ratio of the tube was about 4
(weight ratio of equal lengths of undrawn and drawn tube).
Tubing according to the invention (80/10/10) was subjected to various tests
to determine its capability in the field. Properties of This single-wall
(S/W) composition, O.D. 3.4 mm, I.D. 1.32 mm, are given in Table I below
and compared with the currently commercially available over-extruded NONEL
tube (O/E). The tests included oil immersion, hoop strength, sunshine
exposure, shrinkage and propagation under crimp, powder migration and pull
out tests.
TABLE I
______________________________________
Property O/E NONEL S/W
Oil Resistance
15-23 days 15 days
Hoop Strength (psi)
(Radial Burst)
25.degree. C. 1400 1500
40.degree. C. 1100 1250
65.degree. C. 500 925
Sunshine Exposure
42 7
for two days (32.degree. C.)
then fired:-
bursts/100 meters
Crimp Shrinkage
80.degree. C. for 1 hour
Linear (%) 8.5 1-3
Crimp 5.4 mm 0.8 to 0.5 mm 0.9 to 0.8 mm
Firings after 5/5 fail 0/5 fail
85.degree. C. for 2 hours
Abrasion 30 turns 71 turns
Notch Test 7 kg at 60% 17 kg at 230%
Powder Migration
5% from 18 mg/m
5% from 18 mg/m
Pull through 5.4 mm
9.2 kg at 340%
14.7 at 66%
detonator crimp
(load, elongation)
______________________________________
EXAMPLE VI
Two compositions were made as before using Dowellex 2045A LLDPE and
Primacor EAA, one containing EVA (80/10/10) and one without (43/0/10). The
former was extruded at a high temperature profile (greater than
190.degree. C.) whilst the latter was extruded at a lower temperature
profile (less than 190.degree. C.) at a draw down ratio of 6:1 to give
tubing having the properties indicated in Table II.
TABLE II
______________________________________
Composition 80/10/10 90/0/10
Tube Size: O.D. 3.00 to 3.07 mm
3.00 to 3.07 mm
I.D. 1.37 mm 1.35 mm
Plastic Weight 5.26 g/m 5.26 g/m
Coreload 18.2 mg/m 18.7 mg/m
Powder Migration
5.4% 6.9%
Hoop Strength 1620 psi 1540 psi
Abrasion Resistance
60 turns 60 turns
Shrinkage: 1 hr 80.degree. C.
3.5% 3.3%
Tensile Strength:
Breakload 33.8 kg 34.9 kg
Elongation 380% 390%
Perforations/100 m
295* 154*
Black background,
3.5 hr, air temp.
32.degree. C., bright sunshine
______________________________________
*NB: Commercially available NONEL yields 470 holes under the same
conditions
Thus it is apparent that a melt strength additive (EVA) may be dispensed
with by appropriate control of the extrusion conditions.
The effect of varying melt conditions while retaining the presence of EVA
(CIL 605-V) in a similar 80/10/10 blend (2045-A/605-V/1430), drawn down at
14:1, with a terminal line speed of 40-45 m/min was investigated and the
results are shown in the following Table III
TABLE III
______________________________________
Sample 1 2 3 4
______________________________________
Melt Temp (.degree.C.)
190 177 168 160
Coreload (mg/m) 18 19.6 19 20.6
Powder Migration (%)
3 3.2 3.1 1.1
Shrinkage: 3 3.5 3.4 3.6
1 hr 80.degree.C. (%)
Hoop Strength (psi)
1550 1400 1475 1475
Breakload (kg) 35 31 30 31
Elongation (%) 460 490 460 460
Tensile Strength
63 52 54 53
(N/mm.sup.2)
Diameter Control
Good Poor Poor Poor
______________________________________
In the following Examples listed in Table IV a variety of compositions of
this invention based mostly on olefinic polymers (matrix) are described
and these are respectively: Example VII Dowellex 2045-A; Example VIII Esso
3121.73; Example IX Dow ULDPE-4001; Example X Aecithene LF 3020P; Example
XI Dow 2049 LLDPE; Example XII Dow 2075 LLDPE; Example XIII Du Pont 12J1,
(all 80%), Example XIV Dowellex 2045-A (90%). Examples VII-XIV contain
Primacot 1430 (EAA) (10%) as reactive material adhesion enhancer and all
but XIV contain CIL 605-V (EVA) (10%) as melt strength enhancer. Example
XV uses CIL 605-V as matrix polymer (90%) with Primacor 1430 (10%) as
adhesion promoter whilst XVI uses Du Pont 29-08 HDPE (50%), CIL 605-V
(40%) and Primacor 1430 (10%). All these compositions were made at a melt
draw down ratio of 8:1 and from this Table it can be recognised that a
variety of polymers hitherto thought to be unsuitable for use in shock
wave conductors can be made to work as blends.
TABLE IV
______________________________________
Example VII VIII IX X XI
______________________________________
Tube Size:
O.D. (mm) 3 3 3.1 3.1 2.8
I.D. (mm) 1.3 1.4 1.4 1.4 1.2
Hoop 1550 1310 1200 1350 1745
Strength (psi)
Abrasion 42 46 28 43 50
Resistance (turns)
Shrinkage 2.7 2.3 5.1 4.1 2.2
1 hr 80.degree. C. (%)
Tensile 63 64 44 53 74
Strength (N/mm.sup.2)
Breakload (kg)
35 35 27 32 36
Elongation (%)
460 500 500 590 370
______________________________________
Example XII XIII XIV XV XVI
______________________________________
Tube Size:
O.D. (mm) 3 2.8 2.9 3.1 N/A
I.D. (mm) 1.3 1.3 1.2 1.4 N/A
Hoop 1560 1560 1550 1180 N/A
Strength (psi)
Abrasion 40 46 47 31 N/A
Resistance (turns)
Shrinkage 3.4 2.6 3.6 4.6 N/A
1 hr 80.degree. C. (%)
Tensile 61 67 64 47 N/A
Strength (N/mm.sup.2)
Breakload (kg)
34 33 34 28 N/A
Elongation (%)
440 420 450 280 N/A
______________________________________
N/A = data not available
Further tests were carried out using Aecithene LLDPE's, LF3020, MFI 1.0,
density 918; LC3081, MFI 0.6, density 920; and LF3100 MFI 0.5, density
918, in comparison with the Dowellex 2045-A mentioned above and the
results are indicated in the following Table V. The extrusion was run at
65 rpm and the line speed was 13.2 m/min. The temperature of extrusion was
changed from high profile melt temperature i.e. about 210.degree. C. to
low profile melt temperature i.e about 190.degree. C. As in previous
examples blend composition is indicated as % matrix polymer/% melt
strength enhancer (605-V)/% adhesion enhancer (1430) i.e. in these
examples 80/10/10 shown as A or 90/0/10 as B. The melt draw down ratio was
either 6:1 or 17:1 as indicated.
TABLE V
______________________________________
Example XV11 XVIII IXX XX XXI
______________________________________
Matrix 2045-A 2045-A 3020 3020 3020
Blend A B A B A
Profile High Low Low Low High
ddr 6:1 6:1 6:1 6:1 6:1
Tube Size:
O.D. (mm) 3 3 3 3 3
I.D. (mm) 1.3 1.3 1.3 1.4 1.3
Plastic (g/m)
5.26 5.26 5.2 5.3 5.2
Coreload (mg/m)
18.2 18.7 17.8 13.6 None
Migration (%)
5.4 6.9 7.5 0 --
Hoop 1620 1540 1500 1420 1485
Strength (psi)
Abrasion 60 60 53 62 56
Resistance (turns)
Shrinkage 3.5 3.3 5.5 5.8 5.8
1 hr 80.degree. C. (%)
Tensile 33.8 34.9 N/A 36.1 34.7
Breakload (kg)
Elongation (%)
380 390 N/A 560 580
______________________________________
Example XXII XXIII XXIV XXV
______________________________________
Matrix 3081 3100 3020 3100
Blend A A B B
Profile Low High High High
ddr 6:1 6:1 17:1 17:1
Tube Size:
O.D. (mm) 3 3 3 3
I.D. (mm) 1.3 1.4 1.3 1.3
Plastic (g/m) 4.8 5.7 5.3 5.3
Coreload (mg/m)
None None 15.2 16.6
Migration (%) -- -- 2.75 2.6
Hoop 1390 1400 1490 1405
Strength (psi)
Abrasion 32 59 62 63
Resistance (turns)
Shrinkage 4.6 5.1 5.2 5.86
1 hr 80.degree. C. (%)
Tensile 33.1 34.1 32.2 28.5
Breakload (kg)
Elongation (%)
295 570 641 500
______________________________________
In the following Table VI the physical properties of additional examples of
shock wave conductors made in accordance with the present invention are
described. The compositions were all based on 80% Dowellex LLDPE 2045-A
and 10% CI L EVA 605-V with 10% of a reactive particle adherence promoting
material selected from commercially available ionomer resins, i.e.
neutralised ethylene/methacrylic acid (Surlyn or Nucrel) or
ethylene/acrylic acid (Primacor) resins.
TABLE VI
______________________________________
Example XXVI XXVII XXVIII IXXX
______________________________________
Components (%):
LLDPE 2045-A
80 80 80 80
EVA CIL 605-V
10 10 10 10
Surlyn 1855 10 -- -- --
Nucrel 403 -- -- -- 10
Nucrel 410 -- -- 10 --
Primacor -- 10 -- --
Tube Size:
O.D. (mm) 3.1 3.0 3.1 3.0
I.D. (mm) 1.4 1.3 1.4 1.3
Plastic (g/m)
5.5 5.2 5.3 5.2
Coreload (mg/m)
18.9 17.9 18.6 16.9
Migration (%)
4.5 9.3 12.8 1.6
Shrinkage 2.2 2.6 2.3 2.3
1 hr 80.degree. C. (%)
Tensile 43 48 48 51
Strength (N/mm.sup.2)
Breakload (kg)
26.8 27.2 29.3 29.2
Elongation (%)
690 520 520 510
______________________________________
The above results are quite favourable and in particular the results of
Example IXXX show Nucrel 403 (EMA) to be especially good in minimising
powder migration.
Further work was carried out using different matrix polymers in place of
the LLDPEs illustrated in the foregoing Examples with EVAs and EAAs as
referred to above. Satisfactory tubes were drawn at elevated temperatures
using polypropylene based (80/10/10) compositions. Similar results were
obtained using polyester based (90/10 and 80/10/10) compositions.
EXAMPLE XXX
A polypropylene based tube composed of 80% rubber toughened polypropylene
(90% SHELL GET6100N polypropylene with 10% EXXELOR PE 808
ethylene/propylene copolymer) 10% EVA and 10% EAA (PRIMACOR) was extruded
and cold drawn at a temperature of 150.degree. C. (achieved in a fluidised
bed of glass spheres). The primary tube had an external initial diameter
of 6.3 mm and the drawn tube, at the localised draw point, had an external
final diameter of 2.7 mm. The tube quality was good and powder adhesion
was satisfactory.
A laboratory powder adhesion test using an LLDPE matrix polymer with a
standardized reactive material was used to evaluate a variety of powder
adhesion enhancing materials and the results are reported in Table VII
below
TABLE VII
______________________________________
Powder adhesion enhancing material
(%) Coverage (g/m.sup.2)
______________________________________
EAA (Primacor) 10 3.5-4
Polyisobutylene (Hyvis 30)
1 2
Polyisobutylene (Hyvis 30)
2 3.5
Polyisobutylene (Hyvis 30)
5 9-9.5
Polybutadiene (Lithene N4 6000)
3 5
Polyethylene Wax (AC617A)
5 2
Polyethylene Wax (AC617A)
10 3
EVAL (SOARNOL D) 2 2
EVAL (SOARNOL D) 5 5.9
Portugese WW Gum Rosin
1 2.5-3
______________________________________
In the following Examples higher functionality (9% VA) EVA obtainable under
the trade mark EVATANE was substituted for the EVA (lower VA) used in
earlier Examples with a view to determining the effect on surface coverage
after loading with a standardized powder. The results are indicated in
Table VIII below and it can be seen that compositions B containing
slightly higher functionality EVA than those of compositions A leads to
improved surface coverage but it should be appreciated that significantly
higher VA functionality levels could require adjustment of the extrusion
conditions. However it is interesting to note that use of increased
quantities of EVATANE does not have any marked effect on surface coverage.
This also shows that certain EVAs can function as adhesion promoters in
the bulk polymer matrix.
TABLE VIII
______________________________________
POLYMER
BLEND COMPOSITION %
SURFACE COVERAGE g.m.sup.-2
______________________________________
LLDPE : Lower VA EVA
A1 90:10 1.88
A2 90:10 1.09
A3 90:10 1.09
LLDPE : Higher VA EVA
B1 90:10 2.31
B2 30:20 2.33
B3 60:40 2.74
______________________________________
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